1. Field of the Invention
The present invention is a flexible hermetic sealing. More particularly, this invention is a hermetic seal comprising an encapsulation and a metallic layer that is suitable for use on electronic, optic or opto-electronic hybrid devices.
2. Description of the Prior Art
Electronic components such as transistors, diodes and integrated circuit chips are well known in the prior art. Frequently, these electronic components are formed on a substrate of semi-conducting material such as a silicon or gallium arsenic wafer. Well-known components such as laser diodes and integrated optic chips may also be formed on semi-conducting substrates. Often, optical and electronics components are combined onto a single substrate to reduce cost and simplify manufacturing. These opto-electronic components are especially common in communications systems and in sensing systems such as rotation sensors.
Systems including electrical, optical and opto-electronic components are frequently utilized in industrial and aviation controls. Often, industrial and aviation environments include dust, moisture, industrial chemicals and other contaminants. All of these effects can affect the performance of electronic, optical and opto-electronic components. Moisture, for example, may be absorbed into a component substrate. At low temperatures the moisture absorbed can condense on the surface of a component die and subsequently freeze. The expansion of the water into ice could damage the component or seriously affect component performance. Similarly, corrosive materials, dust or other environmental impurities could impair component performance, or even cause the component to fail. Therefore, it is frequently desirable to isolate the components from environmental effects.
A number of component sealing methods are known in the prior art. Most commonly, the components are protected by coating the chip's surface with a thin dielectric coating such as silicon nitrate. This coating isolates the components from many adverse affects, but has several weaknesses. First, the dielectric coating is incapable of providing a truly hermetic seal, since it is very difficult to apply to the sides of dies. Gaps may occur in the coating, components may come into contact with moisture and impurities that penetrate the coating through the gaps. Another disadvantage of the dielectric coating is the coating material has a different thermal expansion coefficient than the substrate to which it is applied. As the two substances expand or contract with changes in temperature, the different rates of expansion could cause cracks to appear in the coating. These cracks could allow moisture to penetrate the chips. Moreover, the protection of a dielectric coating is "chip-level", or applied to an entire chip. This style of coating is particularly difficult to apply to multiple fiber or multi-array fiber optic systems, which require many fiber connections within a particular component.
Several types of hermetic seals are well-known in the prior art. For example, U.S. Pat. No. 5,262,364 issued to Richard Brow and Larry Kovacic on Nov. 16, 1993 describes a hermetic seal comprising a metallic cover on a glass seal. Other methods of hermetic sealing include fabricating a solid weld around the package, sealing the package in glass, and sealing the package in solder. Each of these sealing methods, however, is very rigid. Stresses applied to optical connections, for example, that are sealed by any of these techniques could damage or break the fiber connections. Additionally, thermal expansion or contraction could cause rigid coatings to crack or break.
From the above description, it should be readily apparent that there is needed a flexible sealing for electrical, optical and opto-electrical components that is capable of forming a hermetic component level seal.